In recent years, supercritical fluid chromatography (hereinafter SFC) has been gaining attention. The SFC is chromatography that is performed by applying constant temperature and pressure to carbon dioxide or the like to obtain a supercritical fluid, and by using the supercritical fluid as a solvent. Supercritical fluid has characteristics of both liquid and gas, and is characterized by being more diffusive and less viscous than liquid. Using such a supercritical fluid as a solvent allows fast, high-separation, high-sensitivity analysis.
In supercritical fluid chromatograph, liquid carbon dioxide is used for a mobile phase. At this time, a modifier (organic solvent, mainly methanol) is added for the purpose of adjusting the degree of separation of a sample, and the mixed liquid is delivered. In order to keep the mobile phase carbon dioxide in a liquid state, it is necessary to set the pressure in the system to 10 MPa or more. For this reason, in the SFC device, a pressure control valve for maintaining the channel system at a constant pressure of 10 MPa or more is provided at a later stage of an analytical column.
By connecting a mass spectrometry (MS) to an SFC to realize a structure of SFC-MS, the detection sensitivity and the identification sensitivity may be increased. In the case of the structure of SFC-MS, the MS is connected to a downstream side of a pressure control valve, and components to be examined, which have been separated in time by a separation column, inevitably pass through the pressure control valve. When a dead volume not included in the flow path of a mobile phase exists in the pressure control valve, the mobile phase stagnates in the dead volume and the components which have been separated in time by the separation column get mixed together, and accurate analysis of the mixed components by the MS is disabled.
Therefore, a pressure control valve that can perform pressure control with high resolution while reducing the dead volume of the pressure control space by finely controlling the gap between the membrane and the plane has been proposed (See Patent Document 1).